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Analog Clock

Frinavale
9,735 Recognized Expert Moderator Expert
This whole thing started when I wanted to display list items in a circle...it just looked way too much like a clock. So for fun I started to create a JavaScript Analog clock.

I was wondering how to draw a line using JavaScript. Everything I've found so far seems to use some JavaScript library....is there an easier way to do this?

Here's what I have so far. I know the clock is Side Ways....but when I try to change the angle so that 12 is at the top (by setting it to -90 or 270 since it's in the 3 o'clock position) it isn't right. Maybe my math is wrong or something?

Expand|Select|Wrap|Line Numbers
  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
  2. "http://www.w3.org/TR/html4/strict.dtd">
  3. <html xmlns="http://www.w3.org/1999/xhtml">
  4.  
  5. <head>
  6.  <style type="text/css">
  7.   li{
  8.    position:absolute;
  9.    list-style:none;
  10.    text-align:center;
  11.    color:#CCCCCC;  
  12.   }
  13.  </style>
  14. </head>
  15. <body>
  16.  
  17.  <ul>
  18.   <li>12</li>
  19.   <li> . </li>
  20.   <li> . </li>
  21.   <li> . </li>
  22.   <li> . </li>
  23.   <li>1 </li>
  24.   <li> . </li>
  25.   <li> . </li>
  26.   <li> . </li>
  27.   <li> . </li>
  28.   <li>2 </li>
  29.   <li> . </li>
  30.   <li> . </li>
  31.   <li> . </li>
  32.   <li> . </li>
  33.   <li>3 </li>
  34.   <li> . </li>
  35.   <li> . </li>
  36.   <li> . </li>
  37.   <li> . </li>
  38.   <li>4 </li>
  39.   <li> . </li>
  40.   <li> . </li>
  41.   <li> . </li>
  42.   <li> . </li>
  43.   <li>5 </li>
  44.   <li> . </li>
  45.   <li> . </li>
  46.   <li> . </li>
  47.   <li> . </li>
  48.   <li>6 </li>
  49.   <li> . </li>
  50.   <li> . </li>
  51.   <li> . </li>
  52.   <li> . </li>
  53.   <li>7 </li>
  54.   <li> . </li>
  55.   <li> . </li>
  56.   <li> . </li>
  57.   <li> . </li>
  58.   <li>8 </li>
  59.   <li> . </li>
  60.   <li> . </li>
  61.   <li> . </li>
  62.   <li> . </li>
  63.   <li>9 </li>
  64.   <li> . </li>
  65.   <li> . </li>
  66.   <li> . </li>
  67.   <li> . </li>
  68.   <li>10</li>
  69.   <li> . </li>
  70.   <li> . </li>
  71.   <li> . </li>
  72.   <li> . </li>
  73.   <li>11</li>
  74.   <li> . </li>
  75.   <li> . </li>
  76.   <li> . </li>
  77.   <li> . </li>
  78.  </ul>
  79.  <div id="time" style="position:absolute; top:280px;"></div>
  80.  <script type="text/javascript">
  81.  
  82.  drawClock();
  83.  drawTime();
  84.  
  85.  
  86.  function drawTime(){
  87.   var listElements = document.getElementsByTagName("li");
  88.   for(var i=0; i<listElements.length; i++){
  89.    listElements[i].style.color="#CCCCCC";      
  90.    listElements[i].style.fontWeight="normal";
  91.    listElements[i].style.border="none";
  92.   }
  93.   var d = new Date();
  94.   var second = d.getSeconds();
  95.   var hour = d.getHours();
  96.   var minute = d.getMinutes();
  97.  
  98.   document.getElementById("time").innerHTML=hour+":"+minute+":"+second;
  99.   if(hour>12){hour -= 12;}
  100.   hour=hour*5;
  101.  
  102.   listElements[hour].style.color="blue";
  103.   listElements[hour].style.fontWeight="bold";
  104.   listElements[hour].style.border="solid 1px blue";
  105.   listElements[minute].style.color="green";
  106.   listElements[minute].style.fontWeight="bold";
  107.   listElements[minute].style.border="solid 1px green";
  108.   listElements[second].style.color="orange";
  109.   listElements[second].style.border="solid 1px orange";
  110.  
  111.  
  112.   setTimeout(drawTime,1000);
  113.  }
  114.  
  115.  function drawClock(){
  116.   var listElements = document.getElementsByTagName("li");
  117.   var step = (2*Math.PI)/listElements.length;
  118.   var angle=0;
  119.   //angle=180.60;//<--sets 12 to the 12 o'clock position ?? not sure why
  120.   var circleCenterX = 120;
  121.   var circleCenterY = 120;
  122.   var radius = 120;
  123.   for(var i = 0; i<listElements.length; i++)
  124.   { 
  125.     var element = listElements[i];
  126.     var left=Math.round(circleCenterX+radius*Math.cos(angle));
  127.     var top=Math.round(circleCenterY+radius*Math.sin(angle));
  128.     element.style.left = left+"px";
  129.     element.style.top = top+"px";
  130.     angle+=step;   
  131.   }
  132.  }
  133.  
  134.  </script>
  135. </body>
  136. </html>
Thanks!

-Frinny
Dec 16 '09 #1
7 5004
Dormilich
8,658 Recognized Expert Moderator Expert
but when I try to change the angle so that 12 is at the top (by setting it to -90 or 270 since it's in the 3 o'clock position) it isn't right.
well, it works for me. (OK, if I use it in rad, aka 270° = 1.5*Math.PI)
Dec 16 '09 #2
Frinavale
9,735 Recognized Expert Moderator Expert
Thanks Dorm. Using 1.5*Math.PI properly set 12 at the 12 o'clock position.

Expand|Select|Wrap|Line Numbers
  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
  2. "http://www.w3.org/TR/html4/strict.dtd">
  3. <html xmlns="http://www.w3.org/1999/xhtml">
  4.  
  5. <head>
  6.  <style type="text/css">
  7.   li{
  8.    position:absolute;
  9.    list-style:none;
  10.    text-align:center;
  11.    color:#CCCCCC;  
  12.   }
  13.  </style>
  14. </head>
  15. <body>
  16.  
  17.  <ul>
  18.   <li>12</li>
  19.   <li> . </li>
  20.   <li> . </li>
  21.   <li> . </li>
  22.   <li> . </li>
  23.   <li>1 </li>
  24.   <li> . </li>
  25.   <li> . </li>
  26.   <li> . </li>
  27.   <li> . </li>
  28.   <li>2 </li>
  29.   <li> . </li>
  30.   <li> . </li>
  31.   <li> . </li>
  32.   <li> . </li>
  33.   <li>3 </li>
  34.   <li> . </li>
  35.   <li> . </li>
  36.   <li> . </li>
  37.   <li> . </li>
  38.   <li>4 </li>
  39.   <li> . </li>
  40.   <li> . </li>
  41.   <li> . </li>
  42.   <li> . </li>
  43.   <li>5 </li>
  44.   <li> . </li>
  45.   <li> . </li>
  46.   <li> . </li>
  47.   <li> . </li>
  48.   <li>6 </li>
  49.   <li> . </li>
  50.   <li> . </li>
  51.   <li> . </li>
  52.   <li> . </li>
  53.   <li>7 </li>
  54.   <li> . </li>
  55.   <li> . </li>
  56.   <li> . </li>
  57.   <li> . </li>
  58.   <li>8 </li>
  59.   <li> . </li>
  60.   <li> . </li>
  61.   <li> . </li>
  62.   <li> . </li>
  63.   <li>9 </li>
  64.   <li> . </li>
  65.   <li> . </li>
  66.   <li> . </li>
  67.   <li> . </li>
  68.   <li>10</li>
  69.   <li> . </li>
  70.   <li> . </li>
  71.   <li> . </li>
  72.   <li> . </li>
  73.   <li>11</li>
  74.   <li> . </li>
  75.   <li> . </li>
  76.   <li> . </li>
  77.   <li> . </li>
  78.  </ul>
  79.  <div id="time" style="position:absolute; top:280px;"></div>
  80.  <script type="text/javascript">
  81.  
  82.  drawClock();
  83.  drawTime();
  84.  
  85.  
  86.  function drawTime(){
  87.   var listElements = document.getElementsByTagName("li");
  88.   for(var i=0; i<listElements.length; i++){
  89.    listElements[i].style.color="#CCCCCC";      
  90.    listElements[i].style.fontWeight="normal";
  91.    listElements[i].style.border="none";
  92.   }
  93.   var d = new Date();
  94.   var second = d.getSeconds();
  95.   var hour = d.getHours();
  96.   var minute = d.getMinutes();
  97.  
  98.   document.getElementById("time").innerHTML=hour+":"+minute+":"+second;
  99.   if(hour>12){hour -= 12;}
  100.   hour=hour*5;
  101.  
  102.   listElements[hour].style.color="blue";
  103.   listElements[hour].style.fontWeight="bold";
  104.   listElements[hour].style.border="solid 1px blue";
  105.   listElements[minute].style.color="green";
  106.   listElements[minute].style.fontWeight="bold";
  107.   listElements[minute].style.border="solid 1px green";
  108.   listElements[second].style.color="orange";
  109.   listElements[second].style.border="solid 1px orange";
  110.  
  111.  
  112.   setTimeout(drawTime,1000);
  113.  }
  114.  
  115.  function drawClock(){
  116.   var listElements = document.getElementsByTagName("li");
  117.   var step = (2*Math.PI)/listElements.length;
  118.   var angle=1.5*Math.PI;
  119.   var circleCenterX = 120;
  120.   var circleCenterY = 120;
  121.   var radius = 120;
  122.   for(var i = 0; i<listElements.length; i++)
  123.   { 
  124.     var element = listElements[i];
  125.     var left=Math.round(circleCenterX+radius*Math.cos(angle));
  126.     var top=Math.round(circleCenterY+radius*Math.sin(angle));
  127.     element.style.left = left+"px";
  128.     element.style.top = top+"px";
  129.     angle+=step;   
  130.   }
  131.  }
  132.  
  133.  </script>
  134. </body>
  135. </html>

-Frinny
Dec 17 '09 #3
Dormilich
8,658 Recognized Expert Moderator Expert
mathematical note:
all trigonometric and exponential function use unit-less parameters by default.

in case of the circle, 2π represents the full circle (same as 360°).
reason: c = 2π·r, by dividing c by r (to make the circumference independent (and unit-less)) you get 2π for a full circle, always. q.e.d.

in case of exponential function you can argue, that the exponent is the number, a value is multiplied with itself and naturally this number (the repetition times) is unit-less.

extending trigonometric functions from exponential functions: complex numbers can be written either trigonometric or exponential style, which uses the angle as parameter.
r·cos(φ) + i·r·sin(φ) = r·exp(iφ)
thus, if the exponential style can’t use unit-bearing values, the trigonometric can’t either.
Dec 17 '09 #4
Frinavale
9,735 Recognized Expert Moderator Expert
Thanks for the refresher Dorm. I actually had to look up all of that stuff yesterday because it's been such a long time since I've used trig.

I think I might be getting closer to finding an answer to my original question: "how do you draw a line".

I think the answer might be to use the HTML5 canvas.

:)

-Frinny
Dec 17 '09 #5
Dormilich
8,658 Recognized Expert Moderator Expert
canvas seems like a good idea. JavaScript was not made for drawing to begin with. you may also think about using SVG graphics in XHTML.

SVG/HTML @ MDC
Dec 17 '09 #6
Frinavale
9,735 Recognized Expert Moderator Expert
*Sigh* Internet Explorer...
When will MS get their *stuff* together enough to keep up!
Whatever...I'm dedicating today to learning about the <canvas> and the rest of the new features offered in HTML 5.

I know JavaScript and HTML weren't actually supposed to be used for what I want to do (draw lines etc). I was toying with the idea of putting a whole bunch of <span>s or maybe some inner lists so that I could simulate drawing a line using these HTML elements....but I didn't like the idea. The other idea I had was to use images...but didn't like that idea either (my images would have to be angled properly and I don't think I have the graphics skills to do this using Paint or Gimp). So the <canvas> looks very appealing to me :)

-Frinny
Dec 17 '09 #7
Dormilich
8,658 Recognized Expert Moderator Expert
found a JS drawing library by chance:
High Performance JavaScript Vector Graphics Library

cross browser compatible, but not compareable to vector graphics.
Dec 18 '09 #8

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